Why does CH3OH have a higher boiling point than Cl2? Explain in terms of intermolecular forces. Select the single best answer. Because CH3OH is soluble in water, and Cl2 is not. ? Because CH2OH can form hydrogen bonds, and Cl2 cannnot. ? Because CH2OH is a liquid, and Cl2 is a gas. Because CH2OH is an ionic compound, and the ion-ion attractions are much stronger than the dispersion forces between Cl2 molecules. X
The Correct Answer and Explanation is:
Correct Answer: Because CH₃OH can form hydrogen bonds, and Cl₂ cannot.
Detailed Explanation:
The difference in boiling points between CH₃OH (methanol) and Cl₂ (chlorine gas) is due to the type and strength of intermolecular forces acting between their molecules.
Intermolecular Forces Overview:
Intermolecular forces are attractions between molecules and directly affect physical properties such as boiling points. There are three main types:
- London dispersion forces (present in all molecules, especially nonpolar ones like Cl₂),
- Dipole-dipole interactions (between polar molecules), and
- Hydrogen bonding (a special, strong type of dipole-dipole force occurring when H is bonded to N, O, or F).
CH₃OH (Methanol):
- Polar molecule with an –OH (hydroxyl) group.
- Can form hydrogen bonds due to the highly electronegative oxygen atom bonded to hydrogen.
- These hydrogen bonds are strong intermolecular attractions that require more energy to break, leading to a higher boiling point.
- Also experiences dipole-dipole interactions and London dispersion forces, but hydrogen bonding is dominant.
Cl₂ (Chlorine Gas):
- Nonpolar molecule consisting of two identical chlorine atoms.
- Can only exhibit London dispersion forces, which are weak and temporary attractions caused by momentary dipoles.
- These weak forces are easier to overcome, so Cl₂ has a much lower boiling point.
Why the Other Options Are Incorrect:
- Solubility in water affects solubility, not boiling point.
- Saying CH₃OH is a liquid and Cl₂ is a gas describes their state at room temperature, not the reason behind their boiling points.
- CH₃OH is not ionic; it is a covalent compound, so ion-ion attractions are not applicable.
Conclusion:
CH₃OH has a higher boiling point than Cl₂ because it can form hydrogen bonds, which are stronger than the London dispersion forces that exist between Cl₂ molecules.
